The short answer to this question is yes and no.
As a general rule if you get pulled over by police department A and are issued a written warning, then later you are pulled over by police department B, police department B will have no way of knowing you were issued a warning by police department A. The same goes if you are issued a warning ticket by Police in Illinois. Then you get pulled over in Iowa. Iowa will not know about the written warning issued in Illinois.
However...here are some exceptions
Again this will vary from agency to agency..
When I worked as a dispatcher for the Illinois State Police, they did not issue verbal warnings. If you received a written warning it would be entered into the computer system and would be automatically deleted after 2 years IF you received no other written warnings or citations by the State Police for 2 years. If you did receive another written warning or citation by the ISP the 2 year period would start all over again.
The above warning information was kept in a data base called TIPS (which stood for Traffic Information and Planning System) This data base is only accessible by the ISP or an ISP agency, IE conservation, Secretary of State Police.
Local police departments had no access to this information and we were not allowed to give it to them.
I now work for a local police department as a dispatcher and we have no State wide data base to enter warning tickets into. If you are pulled over by another officer from the agency I work for I would have to tell the officer that you were issued a warning on such and such date for such and such.
Some area's are serviced by a regional dispatch center (which could dispatcher for several cities or an entire county) which could log warning tickets into a shared computer system for all of the agencies that they dispatch for. This warning information would not be shared with agencies not serviced by this dispatch center.
The dmv in your state will track citations issued to you for at least the last year and this information can be viewed by any officer that runs your drivers license.
So as a general rule if you are issued a warning by agency A then later get pulled over by agency B, agency B will have no way of knowing about the warning you received from agency A.
Good luck.